Workers' Compensation Expense (Schedule of Amounts Recognized in Balance Sheet) (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Accrued Workers' Compensation [Line Items]
Total obligations	$ 231,718	$ 194,347
Less amount included in accrued expenses	16,119	20,044
Noncurrent obligations	215,599	174,303
Occupational disease costs
Accrued Workers' Compensation [Line Items]
Occupational disease costs	158,325	118,900	$ 122,426
Traumatic and other workers’ compensation claims
Accrued Workers' Compensation [Line Items]
Occupational disease costs	$ 73,393	$ 75,447